Not applicable.
This invention relates to the field of modulating the transport of compounds from a cell through a membrane protein. More specifically, the invention relates to modulating the transport of compounds from a cell that overexpresses a MXR gene, but does not overexpress a Pgp gene, with an acridine derivative. The invention also relates to the treatment of a mammal suffering from a cancer that overexpresses a MXR gene but does not overexpress a Pgp gene through the co-administration of an acridine derivative and a chemotherapeutic. The acridine derivatives cited in this invention were previously reported to inhibit MDR-1. Surprisingly these acridine derivatives also inhibit MXR as well. Thus, the acridine derivatives cited in this invention are useful as multi-specific antagonists against cells displaying a MDR phenotype.
Cancer is a leading cause of death (Ihde and Longo, in Chapter 63 of Harrison s Principles of Internal Medicine, 14th edition (1998) (Fauci et al., eds.). In the United States over a half-million people die each year from cancer, accounting for over 20% of all deaths. Cancer is already the leading cause of death in Japan and is expected to be the leading cause of death in the United States sometime next century. Some progress has been made in the treatment of cancers with the use of chemotherapeutic drugs. Antitumor activities have been identified in drugs classes such as antimetabolites, plant alkaloids, topoisomerase inhibitors, and alkylating agents (Slapak and Kufe, in Chapter 86 of Harrison""s Principles of Internal Medicine (1998)).
Unfortunately, cells and tumors often become resistant to drugs and chemotherapeutics during treatment (Slapak and Kufe, supra). Cells and tumors that have been exposed to a single agent become resistant to the agent""s effects (e.g., cytotoxicity). Moreover, cells that become resistant to the treatment of a single agent, such as a cytotoxic chemotherapeutic, often are also resistant to compounds that are unrelated structurally or functionally. This phenomenon is known as multi-drug resistance (MDR). Some studies suggest there is a poor prognosis for patients suffering from certain cancers, whose tumors exhibit the MDR phenotype.
MDR phenotypes are encountered with drugs such as anthracyclines, vinca alkaloids, epipodophyllotoxins, and taxanes. There appear to be several mechanisms for single-agent drug resistance: increased efflux of the drug from the cell, decreased amounts of activating enzyme, increased drug inactivation, increased amounts of target enzyme and an alteration in the drug target (Slapak and Kufe, supra). The mechanisms for the increased efflux of drug from the cell appear to arise from the overexpression of membrane proteins that can transport the chemotherapeutic out of the cell. Cells displaying a MDR phenotype exhibit energy dependent efflux of the drug out of the cell.
Molecular cloning efforts have begun to define the genes encoding the membrane proteins responsible for the MDR phenotypes. All of the genes identified so far belong to a superfamily of proteins known as the ATP-binding cassette proteins (the ABC transporters). One such membrane transporter is P-glycoprotein (Pgp) or MDR (see generally Gottesman and Pastan, (1993) Annu. Rev. Biochem. 62: 385-427). The gene for Pgp has been cloned and confers a MDR phenotype when overexpressed in cells. (Gros et al. (1986) Nature 323: 728-731; Ueda et al. (1987) Proc. Natl. Acad. Sci. U.S.A. 84: 3004-3008; Guild et al. (1988) Proc. Natl. Acad. Sci. U.S.A. 85: 1595-1599; Pastan et al. (1988) Proc. Natl. Acad. Sci. U.S.A. 85: 4486-4490). In humans, the MDR1 gene (Chen et al. (1986) Cell 47: 381-389) can mediate multidrug resistance, whereas the function of the human MDR2 gene is unknown (Gottseman and Pastan, supra). The murine genes that correspond to the human MDR1 are mdr1a (Gros et al. (1986) Cell 47: 371-380) and mdr1b (Gottesman and Pastan, supra). Pgp substrates include the epipodophyllotoxins (e.g., etoposide and teniposide) and the anthracyclines (e.g., doxorubicin and daunorubicin) (Devita et al. eds., (1997) Cancer: Principles and Practice of Oncology, Section 11). Another gene conferring multi-drug resistance, the multidrug resistance associated protein (MRP) has also been cloned. (U.S. Pat. Nos. 5,489,519 and 5,994,130). MRP has the ability to transport chemotherapeutics such as doxorubicin, vincristine, etoposide and colchicine (Devita et al., supra).
While Pgp and MRP are the most extensively studied drug resistance transporters, the number of newly reported genes suggests the potential involvement of many others in clinical resistance (Gottesman, and Pastan, supra; Loe et al. (1996) Eur. J. Cancer 32A 945-957). The canalicular multispecific organic anion transporter (cMOAT or MRP2), responsible for hepatic transport of bilirubin glucuronide, has been correlated with resistance to cisplatinum and to SN38, the active metabolite of CPT-11 (Koike et al. (1997) Cancer Res. 57: 5475-5479). A number of MRP and cMOAT homologues (MRP3, MRP4, MRPS, MRP6) have been described (Kool et al. (1997) Cancer Res. 57: 3537-3547; Lee et at. (1998) Cancer Res. 58: 2741-2747). Examination of an EST database has revealed evidence of 21 previously unknown ABC transporter genes (Allikmets et al. (1996) Hum. Mol. Genet. 5: 1649-1655).
More recently, another member of the ABC transporter family was identified in sublines of cells which do not overexpress MDR or MRP. This new member of the ABC transporter family confers a MDR phenotype and is known as MXR, BRCP, or ABCP. The breast cancer resistance gene (BCRP) was identified in an Adriamycin-resistant subline of MCF-7 cells (Doyle et al. (1998) Proc. Natl. Acad. Sci. U.S.A. 95: 15665-15670). The mitoxantrone-resistance gene (MXR) was identified in the same subline of MCF-7 cells and in a mitoxantrone-resistant subline of human colon carcinoma cells (Miyake et al. (1999) Cancer Res. 59: 8-13). Both genes are almost identical to ABCP, an ABC transporter gene cloned from human placenta (Allikmets et al. (1998) Cancer Res. 58: 5337-5339). Homologies with other genes such as the white eye pigment gene suggest that BCRP/MXR/ABCP encodes a protein which is a half-transporter molecule requiring dimerization for function (Croop et al. (1997) Gene 185: 77-85; Ewart and Howells (1998) Methods in Enzymology 292: 213-224).
Cell lines overexpressing MXR have resistance to mitoxantrone, anthracyclines, topotecan, and the active metabolite of irinotecan, SN38 (Miyake et al., supra). Mitoxantrone is an antineoplastic anthracenedione topoisomerase inhibitor that is used in the treatment of cancers, such as prostate cancer, acute lymphocytic leukemia, breast cancer, and non-Hodgkin""s lymphoma. (Slapak and Kufe, supra; Physicians"" Desk Reference, 53d edition (1999) pp. 1401-1404). Topotecan, a semi-synthetic analog of campothecin, is also a topoisomerase I inhibitor and is used in the treatment of cancers, such as ovarian carcinoma (Physicians"" Desk Reference, 53d edition (1999) pp. 3058-3061).
Cells transfected with the BCRP/MXA/ABCP gene display reduced rhodamine retention and display a resistance pattern similar to cells which overexpress MXR (Doyle et al., supra). While this is a broad resistance pattern, several notable exceptions include the vinca alkaloids, taxanes and VP-16 (etoposide).
The sensitivity of MDR cells to cytotoxic chemotherapeutic drugs can be restored or reversed if the cells are treated with drugs that block the efflux through the multi-drug transporters. Some drugs known as chemosensitizers or reversal agents (e.g., cyclosporin) are known to block the efflux of chemotherapeutic drugs through Pgp and restore sensitivity to chemotherapeutic drugs. An acridine derivative, GF120918 (N-{4-[2-1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)-ethyl]-phenyl}-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide) (Dumaitre and Dodic, WO 92/12132; Dumaitre and Dodic, U.S. Pat. No. 5,604,237; Dodic et al. (1995) 38: 2418-2426) has been reported to inhibit Pgp-mediated efflux at nanomolar concentrations (Hyafil et al. (1993) Cancer Res. 53: 4595-4062; Boer and Gekeler (1995) Drugs of the Future 20: 499-509; den Ouden et al. (1996) Leukemia 10: 1930-1936; Zhou et al. (1997) Leukemia 11: 1516-1522). Pharmaceutical compositions for the administration of GF120918 and GF120918A, the hydrochloride salt of GF120918, are described in Tong et al., WO 96/11007). GF120918 is a Pgp antagonist identified for its potency in reversing Pgp-mediated resistance (Boer and Gekeler (1995) Drugs of the Future 20: 499-509; Witherspoon et al. (1996) Clin. Cancer Res. 2: 7-12). GF120918 is one of several agents developed as xe2x80x9csecond generationxe2x80x9d Pgp antagonists: compounds with little inherent toxicity which are able to antagonize drug efflux at nanomolar concentrations. GF120918 has been tested in phase I clinical trials and was confirmed to have little toxicity (Witherspoon et al., supra). Using inhibition of rhodamine efflux from circulating CD56+ cells as a surrogate marker for Pgp antagonism, GF120918 was shown in these phase I studies to inhibit Pgp at doses readily achievable in patients (Witherspoon et al., supra).
The development of antagonists against Pgp-mediated drug efflux led to a large number of clinical trials attempting the reversal of drug resistance (Raderer and Scheithauer (1993) Cancer 72: 3553-63; Ferry et al. (1996) Eur. J Cancer 32A: 1070-1081). Yet, despite the relative ease of sensitizing cells to chemotherapy in the laboratory, clinical trials have been disappointing, with no clear support emerging for the use of chemosensitizers in clinical practice (Sandor et al. (1998) Drug Resistance Updates 1: 190-200). One explanation commonly given for the failure of Pgp reversal studies to achieve significant clinical benefit is the presence of other mechanisms of drug resistance. The cloning of new transporters would support this contention. Thus, given the array of ABC transporters (over 200 transporters are predicted for human cells (Ling (1997) Cancer Chemother. Pharmacol. 40: S3-S8)) which may play a role in clinical drug resistance, a multispecific antagonist that is able to inhibit more than one transporter or MDR phenotype would be advantageous.
This invention provides for a method of inhibiting a MXR transporter in a cell overexpressing a MXR gene. Optionally the cell is not overexpressing a Pgp gene. The method involves contacting a cell, which overexpresses a MXR gene, but does not overexpress a Pgp gene, with a compound of formula (I) or salts and solvates thereof: 
In the general formula above, the symbol R0 represents a hydrogen or halogen atom, or a C1-4 alkyl, C1-4 alkoxy, C1-4 alkylthio, amino, or nitro group. The symbol R1 represents a hydrogen or halogen atom, or a C1-4 alkyl, C1-4 alkoxy, or C1-4 alkylthio group. The symbol R2 represents hydrogen or a C1-4 alkyl group. The symbol A represents an oxygen or a sulfur atom or a bond. B represents an unsubstituted C1-4 alkylene chain. The symbols R3 and R4 each independently represent a C1-4 alkoxy group. The compound of formula (I) or a salt or solvate thereof is present in an amount sufficient to inhibit a MXR transporter.
In a presently preferred embodiment, the compound is N-{4-[2-1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)-ethyl]-phenyl}-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide or salts and solvates thereof.
In another aspect, the present invention provides a method of assaying the modulation of the functional effect of a test compound on a cell, that overexpresses a MXR gene. Optionally the cell does not overexpress a Pgp gene by an acridine derivative. The method involves contacting a test compound with said cells which overexpress a MXR gene and do not overexpress a Pgp gene, in the presence and absence of an acridine derivative or its salts and solvates thereof; and measuring the ability of the acridine derivative or its salts and solvates thereof, to modulate the functional effect of the test compound. In a presently preferred embodiment, the acridine derivative is N-{4-[2-1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)-ethyl]-phenyl}-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide or salts and solvates thereof. In some embodiments, the cell has been transfected with a MXR gene or the cell contains a functional MXR gene placed in an expression cassette.
Also provided by the present invention is a method of treatment of a mammal which is suffering from a cancer that overexpresses the MXR gene. Optionally the cell does not overexpress a Pgp gene. The method involves co-administering to a mammal a chemotherapeutic which is recognized by a MXR transporter and an effective amount of an acridine derivative or salts or solvates thereof. In some embodiments, the acridine derivative is N-{4-[2-1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)-ethyl]-phenyl}-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide, or its salts and solvates thereof.